1. Field of the Invention
This invention relates to conveying glass sheets and particularly those that have just been heated to a temperature sufficient for tempering or shaping and tempering and are being delivered to a cooling area where cold tempering medium is applied toward the opposite major surfaces of said curved glass sheets at a rate of flow and pressure sufficient to impart at least a partial temper in the curved glass sheets. This invention also may find use in providing curved rolls having a transverse curvature to which soft glass sheets sag while conveyed thereover.
When glass sheets are conveyed on a roller hearth through a tempering apparatus that includes a heating area, a shaping area and a cooling area in end to end relation to one another, it is important that the surface of the conveying rolls of the roller hearth be of a material capable of withstanding the heat in the area in which the rolls are installed and that does not mar the surface of the glass sheets that it engages. It is also important to minimize the relative sliding between the moving hot glass sheets and the rotating curved rolls that convey the hot glass sheets.
In the heating area, superior rolls, for conveying flat glass sheets by rotation until the sheets are heated sufficiently for shaping and tempering, are composed of a sintered fused silica material that is made by grinding solid fused silica into small particles and then sintering these particles to each other at a temperature below the fusing temperature. Such a material is readily formed into an elongated cylindrical shape required for the rolls of a roller hearth conveyor. In addition, fused silica rolls so formed have a relatively small coefficient of thermal expansion. This latter characteristic is extremely desirable due to the extreme temperature to which the rolls of the roller hearth in the heating area of the tempering apparatus are subjected during use.
Fused silica conveyor rolls of cylindrical shape are suitable for conveying flat glass sheets. However, they provide insufficient areas of support for curved glass sheets, so that glass sheets shaped transversely of the path of movement provided by a conveyor of fused silica rolls of cylindrical shape are free to sag out of their desired transverse shapes during their conveyance.
Furthermore, once the glass sheets are conveyed beyond the heating area on fused silica rolls, the need for rolls having such desirable properties at such elevated temperatures becomes less and it would be practical to use rolls suitable at lower glass engaging temperatures that are less expensive than the fused silica rolls most suitable in higher temperature atmospheres.
When glass sheets are shaped in a shaping area by roll forming as in U.S. Pat. No. 3,701,644 to Robert G. Frank or as in U.S. Pat. No. 4,139,359 to Randall S. Johnson and Terry L. Wolfe after being delivered to a roll forming station located downstream of the heating area where the roller hearth is located, or by press bending as in U.S. Pat. No. 4,015,968 to Robert G. Revells et al, for example, or by inertia sag bending as in U.S. Pat. No. 3,476,540 to George F. Ritter et al., and the curved glass sheets are returned to a conveyor for passage through a cooling area, the sheets must retain their shapes during their delivery through the cooling area. Also scuff marks should be prevented from forming on the surfaces of the curved glass sheets during the passage through the cooling area. The glass sheet tempering art would welcome relatively inexpensive and durable rolls for conveying curved glass sheets into and through the cooling area of a glass sheet tempering apparatus. The glass sheet shaping art would welcome less expensive curved shaping rolls than the solid ceramic rolls disclosed in the aforementioned Frank patent and in the aforementioned Johnson and Wolfe patent.
In addition to maintaining the shape of the curved glass sheets and avoiding the development of scuff marks in the shaping and/or cooling area, it is also desirable to have glass sheet conveyor rolls in the cooling area that occupy a minimum possible portion of the cooling area so as to provide minimum interference with the flow of cold tempering medium toward the opposite major surfaces of the curved glass sheets to be tempered.
2. Description of Patents of Interest
U.S. Pat. No. 1,156,386 to Armstrong discloses a belt idler comprising a bracket supporting a pair of upwardly inclined spindles with an idler pulley rotatably mounted about each of the spindles. The pulleys support the upper run of a V-shaped belt, which is supported on the idler pulleys. Each idler pulley rotates independently of the other idler pulley in response to friction from the moving belt. The belt would interfere with flow of tempering medium, so that this apparatus is not suitable to convey curved glass sheets through a cooling area of glass tempering apparatus.
U.S. Pat. No. 1,516,083 to Curtis discloses a roller conveyor comprising composite rolls of concave elevation. Each composite roll comprises five axles disposed in end to end relation, a roller on each axle, a hub for each roller, four supporting brackets (one for each joint) between adjacent hubs, and means to adjust the tightness between adjacent hubs. The bracket supports intermediate the ends of the composite rolls would inhibit the free flow and escape of tempering medium, if used to convey curved glass sheets through the cooling area of glass tempering apparatus.
U.S. Pat. No. 1,927,849 to Roberts discloses a cloth expander and guide that comprises a shaft device comprising companion shafts angularly related with their inner ends pivotally connected at the center of the shaft device. Such a device would not be suitable to convey curved glass sheets through the cooling area of glass tempering apparatus.
U.S. Pat. No. 2,828,852 to Lorig discloses a roller conveyor comprising certain self-centering rolls of special construction. The special rolls are mounted on a bent shaft and comprise a pair of generally frusto-conical shaped rolls or cylindrical rolls with tapered ends of smaller diameter mounted on the shaft with the small diameter ends adjacent each other. The rolls are connected to rotate at the same angular velocity. However, these rolls are not suitable for apparatus to temper curved glass sheets.
U.S. Pat. No. 2,948,384 to Pate discloses a belt conveyor comprising a plurality of rolls. Each roll includes a plurality of idler rollers mounted in spaced relation along the length of a flexible cable. The latter is stationarily fixed at its ends to a conveyor support framework. The flexible cable is tubular and provided with lubricating fittings for maintaining adequate lubrication for bearing assemblies incorporated in the idler rollers. This apparatus is not suitable for glass tempering.
U.S. Pat. No. 3,550,758 to Stalker discloses an idler roller for conveyor belts with special lubricating structure that includes spiral grooves formed in the sidewalls of each roller to help pressurize lubricant within the grooves when the roller rotates. This apparatus is also unsuitable for glass tempering.
U.S. Pat. No. 3,763,992 to Klenk discloses a conveyor of rollers that extend obliquely of a path of movement to force sheets transported thereover toward a guide at one side thereof. The obliquely extending rollers are driven by stub shafts that extend perpendicular to the path of movement through universal joints. A belt drives the stub shafts in unison. The obliquely extending rollers are of cylindrical shape and would not be suitable for use in conveying bent glass sheets.
U.S. Pat. No. 3,918,774 to Nicholson discloses bowed rolls for use in the paper or textile industries. The rolls comprise an elongated shaft, a series of spools disposed about the shaft for rotation and bearings between the shaft and the spools. Longitudinally split spacers separate adjacent bearings. Each spacer has its opposite ends tapered to abut against surfaces of the side walls of the inner races of said adjacent bearings that are complementarily tapered. There is no teaching of how this apparatus would be suitable to temper glass.
U.S. Pat. No. 3,961,737 to Fatula discloses a self-centering roll having two tubular end rim portions mounted on a straight shaft in spaced relation to one another. Means including a deflectable end web and an inner web including an eccentric hub, bearings mounted on the eccentric hub and a member eccentric with respect to the shaft axis mounted on the outside of the bearing concentric with the bearing axis cause the end rim portions to rotate on axes that intersect at a point intermediate the inner webs and are arranged at the same angle to the shaft axis. The roll of this patent is not curved to conform to the transverse shape of conveyed glass sheets.
U.S. Pat. No. 4,033,497 to Przygocki discloses a segmented billet roll provided with removable and axially adjustable segments having tongue and groove connections that interfit with one another and may be adjusted along the length of a central shaft to lengthen or shorten the length of the billet roll to accommodate for sheets of different widths. Set screws are provided to lock the position of each segment along the length of the central shaft. The billet roll is of cylindrical shape in cross-section for use in handling flat sheets. The tongues and grooves of adjacent segments interfit closely and make parallel sliding contact over the length of the billet roll. The tight, sliding fit limits the use of the interfitting segments to cylindrical rolls.